1. Field of the Invention
The present invention relates to a stroboscopic scanning electron microscope, and more specifically it relates to such a microscope as an electron beam tester for monitoring a working signal waveform in the element of such as a semiconductor integrated circuit device.
2. Description of the Related Art
The integration density of semiconductor devices is continually improving, and semiconductor integrated circuits with a high integration density, such as LSI, VLSI or the like, are now brought into existence. In the manufacturing process of such semiconductor integrated circuits, it is common to test the working performance of the semiconductor element before assembling it within an envelope. The test is carried out by contacting a mechanical probe with a predetermined conductive layer portion of the semiconductor element in order to detect a signal waveform at a connection point (node) between respective circuit blocks while operating the semiconductor element, and by monitoring the waveform on an oscilloscope or the like.
The higher the integration density of the element, the smaller becomes the electrostatic capacitance of the node from which a working signal waveform is derived, due to thinning of the width of an interconnection wire. Thus, the electrostatic capacitance of the mechanical probe itself becomes relatively large, and measurement errors may occur. Further, it is difficult to mechanically contact with the node, so a precise measurement can not be ensured.
For this reason, a measurement has been done by using a non-contact type electron probe. The measurement makes use of a phenomenon that when the primary electron is bombarded upon a measuring point the amount of the secondary electron emitted out from the point varies with the surface potential of the measuring point. The non-contact electron probe is generally called a stroboscopic scanning electron microscope, or an electron beam tester. The electron beam tester comprises a scanning type electron microscope, a measuring control system such as for giving sampling pulses to the scanning type electron microscope for its stroboscopic operation, an element drive system for driving the element to be measured, an image processing system, and the like.
In the stroboscopic scanning electron microscope, however, there gives rise to a problem that a measurement accuracy is degraded under the influence of other interconnecting wires or the like adjacent to the measuring point.